Cervical cancer accounts for nearly 10% of all female cancers and is a leading cause of cancer among women in developing countries (Franco, E. L. et al., Can Med Assoc J. 2001; 164:1017-25). The regions with the highest incidence of the disease are generally those with the greatest mortality and include Central America, Africa, and the Carribean (Ferlay, J. et al., 1998. IARC CancerBase no. 3. Lyon:IARCPress.). Incidence in Europe and North America has declined precipitously over the past 50 years, possibly due to the advent of routine screening by Papanicolaou (Pap) smear testing (reviewed in Franco et al., ibid). Cervical cancer is one of the most preventable cancers, with survival being directly related to the stage of the disease at diagnosis. The 5-year survival rate is 88% for women having initial diagnosis of localized disease as opposed to 13% for women diagnosed with distant disease (Report of the Gynecologic Cancers Progress Review Group, November 2001, National Cancer Institute). More than 50% of women diagnosed with cervical cancer in the U.S. have not had a Pap smear in the past three years (Wright, T. C. et al., JAMA. 2000; 283:81-6).
Pap screening remains the predominant mode of detecting cancerous and precancerous cervical lesions; more than 50 million women undergo Pap screening each year in the U.S. (Wright, T. C. et al., JAMA 2002; 287:2120-29). Despite its widespread use, Pap smear testing is only partially effective; some estimates place the sensitivity of conventional Pap smear testing at 50-60% (Lorincz, A. T. and Richart, R. M., (Arch Pathol Lab Med. 2003; 127:959-68; Nanda, K. et al., 2000. Ann Intern Med 132:810.; Fahey M T, et al. Am J Epidemiol. 1995; 141:680-9; Myers E R, McCrory D C, Subramanian S, et al. Obstet Gynecol. 2000; 96:645-52.) or 70-80% (Clavel, C. et al., 2001. Br J Cancer 84:1616). Recent innovations in cytological screening and sampling, such as liquid-based tests, have improved the sensitivity of these methods to 75-95% (Lorincz, A. T. et al. ibid; Nanda, K. et al., ibid.; Hutchinson M L, Zahniser D J, Sherman M E, et al. Cancer. 1999; 87:48-55.). Nonetheless, even these improved methods fail to detect a significant portion of abnormal, and often precancerous, cells. Once identified, patients with atypical squamous cells of undetermined significance (ASCUS) are subjected to various levels of monitoring and treatment, depending on the particular attendant risk factors and clinical presentation (reviewed in Wright, T. C. et al. JAMA 2002, ibid).
Human Papillomavirus (HPV) has been identified as the primary, and possibly only, cause of cervical cancer (Muñoz N, Bosch F X, de Sanjosé S, et al., Int J Cancer 1992; 52:743-9; Bosch F X, Lorincz A, Munoz N, Meijer Shah K V., Clin Pathol 2002; 55:244-65), implicated in as many as 99.7% of all cases (Wallboomers, J. M. et al., 1999. J Pathol 189:12-19). The HPV genome is an 8 kb, circular, double stranded DNA comprising 8 genes, all encoded on the same strand. As many as 200 different HPV types have been identified in humans (Burd, E. M. Clin Microbiol Rev. 2003; 16:1-17); of these approximately 40 types have been found capable of infecting the genital tract (Munoz, N. N Engl J Med 2003; 348:518-27.). Still further classification has resulted in the identification of high- and low-risk viral types for development of cervical cancer. Estimates place the number of high-risk types between 13-19 strains, with two strains, HPV 16 and 18 together accounting for as much as 55-85% of infections, depending on subject age and geographical location (Munoz, N., ibid). The predominant low-risk strains are HPV 6 and 11; these may lead to genital warts (reviewed in Burd, E. M., ibid).
The elucidation of certain high risk HPV strains as the causative agents of cervical cancer, coupled with advances in molecular biological methods, has expanded the spectrum of methods available for both preventing and detecting HPV infection. Vaccines for the most common high-risk HPV strains are currently in clinical trials (Koutsky, L A. et al., 2002. NEJM 347:1645-51). Moreover, some authorities are calling for HPV DNA screening for use in conjunction with, or in some cases, in lieu of, conventional cytological methods (Wright, T. C. and Schiffman, M. N. Engl. J. Med, 2003; 348: 489-90). Various alternative DNA-based detection methods have been introduced, including the HYBRID CAPTURE II (HCII) test (Digene, Gaithersburg, Md.), which was been approved by the FDA in March, 1999. The HYBRID CAPTURE method relies on hybridization of target DNA to complementary RNA probes. The resultant RNA-DNA hybrids are recognized by surface-bound antibodies as well as antibodies conjugated to alkaline phosphatase, allowing generation of a chemiluminescent signal in the presence of appropriate substrates (Lorincz, A. T. J Obstet Gynaecol Res. 1996; 22:629-36; also U.S. Pat. No. 4,908,306 and related patents and applications). Further alternative methods include the use of sequence specific probes for use in PCR or sandwich hybridization assays, such as those described in U.S. Pat. No. 6,583,278. Other methods rely on various PCR primers for selective amplification of specific strains, as in U.S. Pat. No. 5,447,839 and related applications. Still other methods rely on in situ hybridization of sequence-specific probes to isolated cervical cells, described in WO 00/24760A1 (e.g. INFORM HPV, Ventana Medical Systems, Inc., Tuscon, Ariz.; Qureshi M N et al., Diagn. Cytopathol. 2003; 29:149-155).
Therefore, there exists a need for a rapid, sensitive, and highly quantitative direct detection assay for detecting HPV infection by high risk strains in cervical samples. Given the current reliance on molecular methods, it is likely that there will be an ongoing and increasing need for rapid, quantitative methods of detecting HPV infection.